In the case of joining two resin members by a laser welding, it is necessary to press and fix resin members to each other by the use of a base board to mount the resin members thereon and a jig. Here, the joining method of resin members according to the conventional technology will be explained with reference to FIG. 4. FIG. 4 is an illustration for explaining the joining method of resin members according to the conventional technology and is a cross sectional view of the resin members.
For example, a flat plate-shaped resin member 20 is mounted on a flat plate-shaped base board 22. And then, light absorbing agent 23 is coated on the surface of the resin member 20, and a flat plate-shaped resin member 21 is superposed on the light absorbing agent 23-coated surface of the resin member 20. And then, a flat plate-shaped pressing member 25 made of a light transmissive member, such as glass, is mounted on the resin member 21 so that the two resin members 20 and 21 are sandwiched between the pressing member 25 and the base board 22. On the condition that the resin members 20 and 21 are pressed with the pressing member 25, laser beams 10 are irradiated to the resin members 20 and 21 from above of the pressing member 25. The laser beams 10 pass through the pressing member 25 and the resin member 21, and are irradiated to the light absorbing agent 23. The laser beams 10 are absorbed by the light absorbing agent 23 so that heat is generated on a part (a melting region 24 shown in FIG. 4) and resin on the joined surfaces of the resin member 20 and the resin member 21 is melted, whereby the resin member 20 and the resin member 21 are joined to each other.
In the case of conducting a laser welding, the most of the laser beams pass through the resin member 20. The laser beams 11 having passed through the resin member 20 reach the surface of the base board 22 being the surface coming in contact with the resin member 20. In the case that the surface (the surface coming in contact with the resin member 20) of the base board 22 is made of a material incapable of allowing a laser beam to pass through, the laser beams 11 are scattered about or absorbed on the surface, and heat is generated on the surface (the surface in contact with the resin member 20) of the base board 22. If heat is generated on the surface of the base board 22, the surface of the resin member 20 coming in contact with the surface is melted (a melting region 26 shown in FIG. 4). As a result, there is a fear that the surface shape of the base board 22 may be transferred to the surface of the resin member 20. Especially, in the case that the surface of the base board 22 is rough, if the rough surface patter of the base board 22 is transferred to the surface of the resin member 20, the surface appearance of the component obtained by the joining get deteriorated. The deterioration of the surface appearance results in the deterioration of the quality of external appearance. For example, in the case that an optical detection, evaluation, and the like are conducted by irradiating light beams to a component obtained by a joining process, the deterioration of the quality of external appearance causes a fear to provide adverse effects to the performance of detection and evaluation.
Patent documents 1 discloses a method of joining plastic plates to each other by a thermo-compression bonding, an ultrasonic welding, an adhesive, or a laser welding. However, Patent documents 1 does not disclose a technique to avoid generation of heat on the surface of a base board in a laser welding. Therefore, it is difficult to solve the above problem.
Patent documents 1: Japanese Patent Unexamined Publication No. 2005-74775